Message in a Bottle

The New Horizons probe blasted off for Pluto last week, the start of an ambitious mission that promises to bring us pictures of the solar system's final unexplored planet a decade from now.

If all goes well, New Horizons will begin to answer questions about Pluto and its three moons, the primeval worldlets of the Kuiper Belt, and offer clues to conditions in the earliest days of the solar system. It's a mission whose findings should enchant adults who remember the jaw-dropping Voyager photos from Jupiter and Saturn, and entrance children not even born yet. But even before New Horizons discovers anything, it raises a question we'll have to answer closer to home: What kind of messages should we accompany our space probes?

Such messages date back to Pioneers 10 and 11. Launched in 1973, these twin craft carried plaques designed to tell any beings who found them something about who we were and where we came from. Four years later, the Voyager probes included phonograph records carrying sounds and images of Earth. Those plaques and records are still out there, attached to spacecraft speeding through the silent dark of the solar system's outermost precincts.

It's easy to make fun of this stuff (and I'll do a little of that), but there's also something refreshingly uncynical about these messages in the tiniest of bottles cast into the most unimaginable of oceans. Particularly when you compare them with what we've sent out since then.

The Pioneer probes carried the first message intended to be intelligible by beings who might find the probe many eons and millions of miles later. The Pioneer plaque -- you can see it on this Wikipedia page -- was hurriedly put together by Carl Sagan, Linda Salzman Sagan and Frank Drake, and designed to communicate a lot of information in a small space in a way that could be understood by any species that grasped the basics of physics. It included naked male and female figures and diagrams designed to show the location of Earth in the galaxy and the solar system.

If the plaque were discovered today, aliens might be thrown by a couple of things: There are no rings around Jupiter, Uranus and Neptune; only one human gender seems to have genitalia; and we really needed hair advice in the 1970s. But the Pioneer effort was a bold step, one that paved the way for the Voyagers and their famous "Golden Records."

The Voyagers carried 12-inch, gold-plated copper phonograph records containing 115 images and a wealth of sounds: snippets of the natural world, songs (including an Indian raga, a Navajo chant, Bach, Mozart and "Johnny B. Goode"), spoken greetings in 55 languages, and printed messages from President Carter and (oops) U.N. Secretary General Kurt Waldheim. The record came with a cartridge and phonograph needle, and its cover includes visual instructions about how to make a record player.

Voyager 1 is now far beyond the orbit of Pluto in what scientists call the heliosheath, defined as the area in which the solar wind drops below supersonic speed. Eventually it will reach the heliopause, where the solar wind becomes too weak to push back the flow of rarefied hydrogen and helium gas that fills interstellar space. That's expected to happen around 2015; when it does, Voyager 1 will be the first human-made object to pass beyond the boundaries of our solar system. (And it should still be able to send back data -- the Voyagers are expected to last until 2020 or so.)

Mock the Golden Record if you wish -- and sure, there is something a bit funny about a spacecraft with a phonograph record bolted to it, along with instructions for making a device few American teenagers would recognize. (If you want more ironies, the Golden Record was released as a CD-ROM in 1992, though only on Earth.) But before you do, consider the messages that have gone out with later probes.

The Cassini probe, which is currently exploring Saturn and its moons, was launched with a DVD -- one containing 614,420 signatures. Meanwhile, a rather different message was imagined for the Huygens probe, now resting on the surface of Titan. Jon Lomberg, design director for the Voyager Record (see his Web site at www.jonlomberg.com), pondered sending a message aboard Huygens. His answer, arrived at with help from physicist and science-fiction writer Gregory Benford: a diamond wafer that would survive for billions of yeas after Huygens disintegrated. (Mr. Lomberg calls the wafer an effort to make "an artificial fossil.") The wafer would contain a photograph of people and photographs of astronomical objects intended to help a potential discoverer figure out how old it was.

DeBeers donated diamond wafers and the "Portrait of Humanity" photo was taken, but Cassini went to Saturn without the message, which Mr. Lomberg says was scrapped amid NASA concerns about who'd get credit for the project and the fact that Fuji-Xerox had sponsored it. (He wrote an interesting article about the project for the journal Contact in Context -- you can read it and see the photo here.)

Cassini isn't the only probe bearing signatures. The Stardust probe, which rendezvoused with the comet Wild 2 in 2004, carries microchips engraved with some pictures of mission-team members and more than a million names. Granted, Cassini and Stardust aren't leaving the solar system. New Horizons should be. So what's it carrying? A CD containing more than 435,000 names of people who signed up through a Web site. (As far as I can tell, that's it - a NASA official didn't respond to an email sent last week.)

From records to CDs and DVDs -- hey, we're making technological progress, right? (Though it would be a shame if a future probe carrying a Blu-ray disk were discovered by a civilization that uses the HD-DVD standard, leading to an interstellar war.)

But in terms of messages sent into space, this technological march isn't progress at all. Mr. Lomberg notes that a phonograph record can be read mechanically if the process to do so is reconstructed -- a process the record's cover was designed to explain in universal terms. On the other hand, he says, "a digital encoding system is entirely arbitrary. ... If you don't know the code and don't know the operating system, you can't decipher it from first principles."

A CD is "a very foolish method if what you thought you were doing was communicating with somebody," Mr. Lomberg says. And even if some galactic civilization does manage to conjure up software that lets it read New Horizon's CD, what will it get for its trouble? Names. Lots and lots of undecipherable, meaningless names.

New Horizons, like Stardust and Cassini before it, is a wonderfully exciting mission, and in these days of tight budgets and limited vision, anything that brings it more publicity is to be praised. But ironically, while sending probes unimaginable distances we seem to have lost the long view of what such missions may ultimately mean. The New Horizons CD was meant for us, not for anyone who might find it eons from now -- an oddly blinkered point of view, given it's aboard a probe exploring the cosmos.

In all likelihood, space probes will be the only things of ours that endure after our species is gone and our planet utterly changed -- a few inert, pitted machines will be the sole clues that we ever existed, and the ancient messages they carry our only chance to explain who we were. It's vanishingly unlikely that any being will ever find the Pioneers, Voyagers or the New Horizons probe in the billion-odd years during which their messages will remain readable. But though imagining such a discovery borders on an act of faith, it's not impossible. And since it isn't, shouldn't the only trace of ourselves be something more substantive than an unbelievably ancient PR campaign? Don't we owe ourselves a final testament that's something more than space spam?